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g0201_0300.s0210_course_schedule_ii.readme.md Maven / Gradle / Ivy

210\. Course Schedule II

Medium

There are a total of `numCourses` courses you have to take, labeled from `0` to `numCourses - 1`. You are given an array `prerequisites` where prerequisites[i] = [ai, bi] indicates that you **must** take course bi first if you want to take course ai.

*   For example, the pair `[0, 1]`, indicates that to take course `0` you have to first take course `1`.

Return _the ordering of courses you should take to finish all courses_. If there are many valid answers, return **any** of them. If it is impossible to finish all courses, return **an empty array**.

**Example 1:**

**Input:** numCourses = 2, prerequisites = [[1,0]]

**Output:** [0,1]

**Explanation:**

    There are a total of 2 courses to take. To take course 1 you should have finished course 0.
    So the correct course order is [0,1].

**Example 2:**

**Input:** numCourses = 4, prerequisites = [[1,0],[2,0],[3,1],[3,2]]

**Output:** [0,2,1,3]

**Explanation:**

    There are a total of 4 courses to take. To take course 3 you should have finished both courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0.
    So one correct course order is [0,1,2,3]. Another correct ordering is [0,2,1,3].

**Example 3:**

**Input:** numCourses = 1, prerequisites = []

**Output:** [0] 

**Constraints:**

*   `1 <= numCourses <= 2000`
*   `0 <= prerequisites.length <= numCourses * (numCourses - 1)`
*   `prerequisites[i].length == 2`
*   0 <= ai, bi < numCourses
*   ai != bi
*   All the pairs [ai, bi] are **distinct**.